In electrochemical cells having a negative electrode made completely or partially of lithium, it is known that the electrode's kinetic stability in the presence of a non-aqueous electrolyte only permits a limited number of charge/discharge cycles.
This limitation results, in particular, from the facts that such electrodes are passivated by reacting with the solvent, and also that they grow dendrites; these two phenomena limiting charging efficiency to such an extent that it rarely exceeds 50%.
Remedies have therefore been sought for these drawbacks, and in particular, for improving cycling characteristics in a non-aqueous electrolytic medium.
As an example of such proposed remedies, M. Garreau, J. Thevenin, D. Warin and P. Campion at the "International Workshop on Lithium Non-Aqueous Batteries, Cleveland 1980", proposed using electrodes made of lithium and of aluminum by electroplating lithium onto an aluminum substrate. By solid phase diffusion, the lithium formed a compound of the Li.sub.p Al type, where p is less than unity. When cycling at ambient temperature, this compound is capable of reversibly releasing lithium during the course of more than one hundred charge-discharge cycles, at current densities which may exceed one mA/cm.sup.2, and for cycled capacities of more than 1 mAh/cm.sup.2.
Unfortunately, such an electrode has several drawbacks resulting firstly from the increase in molecular volume of such a compound in comparison with lithium, and secondly from an electrode potential which differs by 350 mV from that of lithium, thereby reducing the free energy of the overall system.
Various other proposals have been made along the same lines, and in particular Li-Si and Li-B alloys have been studied as negative electrode materials for cells operating at high temperature.
However, these alloys have phase transitions and too small lithium activity to have any advantage over lithium/aluminum systems which are also much more reversible.
Further, electrode shedding during cycling is observed with the alloys, which reduces their lifetime. This results from the lithium-receiving structure not being organized.
Proposals have also been made to make a negative electrode from the compound Li.sub.x CaSi.sub.2, where x lies in the range 0 to 4.
However, in all such alloys the reversibility of the lithium-containing electrode remains low and the activity of the lithium remains well below unity.
French published patent specification No. 2,442,514 also proposes using lithium insertion compounds for making the negative electrode, and more particularly using layer structure compounds based on graphite. Specific examples include LiC.sub.6, KC.sub.8, etc. In all cases, the insertion compound has a two-dimensional lattice structure in which the lithium is sandwiched or interposed without true insertion. Such compounds have the drawbacks firstly of having a chemical potential which is fairly far removed from that of lithium, and secondly, and above all, of catalyzing decomposition reactions in electrolytes.
Preferred embodiments of the present invention provide an improved lithium-containing negative electrode structure for use in a rechargeable cell having a non-aqueous electrolyte.